Device for the study of common fractions.



E. C. JACOBS. DEVICE 'FOR THE STUDY OF COMMON FRACTIONS. APPLICATIONFILED DEC. 12, mm RENEWED NOV. 22. 19l6.

1,224,748, Patented May1,1917.

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EDWIN G. JACOBS, OFNORWALK, OHIO.

DEVICE 11011 THE srnnY or COMMON rnAcrIoNs.

Application filed December 12, 1913, Serial No. 806,209. RenewedNovember 22, 1916. Serial No. 132,913.

To all 10. mm it may concern:

e it known that I, EDWIN O. JAcoBs, a citizen of the United States, andresident of Norwalk, in the county of Huron and State of Ohio, haveinvented certain new and useful Improvements in Devices for the Study ofCommon Fractions, of which I hereby declare the following to be a full,clear, and exact description, such as will enable others skilled in theart to which it appertains to make and use the same.

The objects of the invention are to provide a disk or disks graduated tofractional parts of a circle and having fractional quantities displayedthereon in a graphic manner, so as to illustrate at a glance a series offractional parts of a circle, and the relations of the fractional partsto each other, and also includes a base provided with a center pin uponwhich the disks are revoluble.

A ruler is also preferably employed having radial edges extending fromthe center of the disk beyond the circumference by means of which radiallines can be drawn and the corresponding degrees upon the margin can beread.

The invention is designed to assist in the drawing of fractional partsof a circle, and in drawing geometric figures such as stars, the pointsof which are spaced equally apart, and incose equal angles.

The disks may be two or more in number and there may be displayed uponone disk the single orunitary fractions only with arcs of circles, andshowing their relative values, and upon the other disk all the fractionscomprising each unit can be displayed, up to the limit of needed use inordinary school work, or only one disk maybe used if desired,illustrating either method of grouping fractions, or additional diskscan be added to increase the number of fractions, since arcsillustrating all fractions can not be drawn, upon a single disk.

The invention is illustrated in the accompanying drawings, hereinafterfurther described with the method of its use, and is specificallypointed out inthe claims.

In th is a plan view of the device showing one method of its use; Fig. 2is a plan view of a modified form of disk. Fig. 3 is a side elevation ofthe disk and a base plate upon which the disk is mounted.

In Fig. 1 a disk A is shown having the Specification of Letters Patent.

e accompanying drawings Figure 1* Patented May 1, 191?.

degrees of a circle marked upon a graduated tional part of a circle, at45. A ruler R pivoted at the center of the disk at C has a radial edge Rby means of which any radial line can be followed to its correspondingdegree.

The same is true of all the fractional parts, such as the fraction 1/18designated by the numeral 18, and indicated on the graduated margin by20, and as the fraction 1/20 indicated upon the margin by 18 or thefraction 1/7 indicated by the numeral 7 and upon the margin by 51-3/7".In every case the fraction is more simply indicated if it is a single orunitary fraction, by marking only the denominator in the correspondingare which may be long or short provided its marginal radial lines run tothe graduated margin.

For instance, the arc 8 has a radial line at each end and 45 areincluded between them. Also the are 10 has radial lines at each endincluding 36 between them. It is therefore easy for the student to seeat a glance that the difference between l/S, and l/10 is 9 or 1/40 and40 can be marked directly upon this smaller arc as shown in Fig. 1.

Also it is evident the sum of fractions included between two radiiequals the arc included between the same radii since as shown in Fig. 1,

D in degrees and reduced to common fractions, or read on the dial ofFig. 1.

For instance employing the ruler QR first on radial lines L and then onradial line M, a difference of 42 is read between the arcs representing3/10 and 5/12 and equals 7/60. The horizontal line 11 it is understoodis used as a common starting point or base line. The ruler It pivotelupon the center 0 can revolve so that its radial edges register with anyof the radial lines and it should extend beyond the graduated margin.

The disk or dial shown in Fig. 2 can be used in connection with a radialruler R to measure differences between fractions having a unit for anumerator and also to indicate differences between fractions havingplural numbers for numerators.

1n the arringement shown in Fi 1 a great number of arcs of differentlengths can be drawn when the numerators are units, and in thearrangement shown in Fi 2 both units and plural numbers can be used fornumerators. For convenience in use the disk A is mounted upon a base Awhich is provided with a needle A that projects through the center C ofthe disk. The ruler It is also pivoted in this disk and preferablyextends beyond the disk A so that the graduations or any of them can bemarked upon a piece of paper E, inserted between the disk and its baseand from the points thus indicated the various angles of geometricfigures can be drawn to produce stars or other effects.

The radial ruler is provided with regularly spaced openings 0, 0, bymeans of which arcs of circles of specified diameter can be drawn by apupil by inserting the point of a pencil therein. One or more smallholes P, 1 at the left of the center and on the base line are shown inFig. 1, which pass through the disk A, and are used as centers to enablethe pupil to draw a larger circle without the pivoted ruler.

Openings Q, Q are also made at spaced intervals in the disk throughwhich arcs and circles can be drawn if desired.

When, however, the radial ruler is used circles and arcs can be drawnthrough spaced openings 0, 0 therein.

Having described the invention what I claim as new and desire to secureby Letters Patent is:

1. In a device to assist in the study of fractions, a foundation diskhaving a central upwardly extendingpoint, a disk centrally mounted androtatable upon said point, said disk graduated in degrees of a greatcircle upon its edge, said disk having represented thereon radial lines,including fractional. parts of the circle between them Copies of thispatent may be and arcs included between said radial lines, thefractional amount being represented upon each arc in common fractions,and a ruler revoluble upon said center pin and having a radial sideextending beyond the graduated edge, whereby the sum of any pluralnumber of the fractions represented by said arcs and differences betweenthem can be read in degrees of the great circle, and also in divisionsof said arcs.

2. In a device to assist in the study of fractions, in combination, adisk having its outer edge graduated in degrees of a great circle, andprovided with a series of arcs, representing divisional parts of thecircle, and with a representation of a common fraction upon each arc,the limits of each are being designated by radial lines, and a rulerrotatable upon the center of said disk, and having a radial edge,whereby the number of degrees subtended by each arc or portions of anarc can be read upon said graduated margin of said disk.

3. In a device for the graphical representation of operations infractions, a disk having a radial base line extending thereacross, andprovided with a graduated margin, arcs of circles originating in saidbase line and radial lines defining said ares, said arcs designatingfractional parts of the circle, additional radial lines, furthersubdividing some of these arcs, the fractional values of said ares beingrepresented thereon in common fractions, and a pivoted ruler having aradially extended edge, adapted to correspond in turn with said radiallines, and serving to register with the graduations on said graduatededge.

41:. In a device for the graphical representation of operations incommon fractions, and also adapted for the construction of angles ingeometric forms, a centrally pivoted disk, provided with a graduatededge, and a radial base line, a series of arcs, of different lengths,and limiting radial lines therefor represented upon said disk, said arcsdesignated by the denominators of the common fractional parts theyrepresent, and a centrally pivoted ruler having a radial edge adapted toregister with said radial lines in turn and with the graduations on saidedge, and extending beyond said edge, whereby the fractional amountincluded between any two of said arcs or the amount of differencebetween them can be read upon said graduated edge.

In testimony whereof, I hereunto set my hand this 4th day of September,1913.

ED'WIN C.'JACOBS In presence of WM. M. MONROE, Anonsrus W. BELL.

by addressing the Commissioner of Patents,

